The present invention relates to a mold for molding a hollow double-walled product by supplying a cylindrical parison of synthetic resin extruded by the die of an extruder to a position between a pair of male and female mold members, moving the mold members toward each other to pinch and seal the parison therebetween, and injecting air into the parison, and a blow molding apparatus which employs such a mold.
Various processes for manufacturing hollow double-walled products have been developed so far. Examples of such processes are disclosed in Japanese Patent Publications No. 46(1971)-14153, 49(1974)-18748, and 51(1976)-13495.
However, there are known only few molds used to mold hollow double-walled products. There molds are shown in Japanese Patent Publication No. 49(1974)-41111, Japanese Laid-Open Patent Publication Nos. 60(1986)-67130, and 63(1988)-221020.
According to Japanese Laid-Open Patent Publication No. 60(1986)-67130, a mold includes a female mold member having four separate peripheral wall segments and a bottom. When air is injected into the parison, the parison can be smoothly moved along the inner wall surfaces of the peripheral wall segments, so that a double-wall product having a uniform thickness can be molded. Double-walled products thus molded are stronger than those produced by conventional molds. All of the four peripheral wall segments are swingable outwardly, and they are required to swing in timed relation to the injection of air into the parison. The mold and a molding apparatus using the mold are therefore complex and expensive. Another problem is that a product molded by the mold has burrs on all four corners thereof. Though the molded product has a sufficient degree of mechanical strength, the burrs have to be removed in a subsequent step, and the product needs to be improved for its commercial value.
The mold disclosed in Japanese patent Publication No. 49(1974)-4111 is only limited to the fabrication of a product having a body and a lid which share a hinge. This mold is therefore less versatile. The hinge of the molded product tends to be thin.
The mold shown in Japanese Laid-Open Patent Publication No. 63(1988)-221020 also lacks versatility because it is used exclusively to form undercuts on molded parts.